Emitting materials used in organic electroluminescent devices (OLEDs) are frequently organometallic complexes which exhibit phosphorescence. For quantum-mechanical reasons, up to four times the energy efficiency and power efficiency is possible using organometallic compounds as phosphorescent emitters. In general terms, there is still a need for improvement in OLEDs, especially also in OLEDs which exhibit phosphorescence, for example with regard to efficiency, operating voltage and lifetime.
The properties of phosphorescent OLEDs are not just determined by the triplet emitters used. More particularly, the other materials used, for example matrix materials, are also of particular significance here. Improvements to these materials can thus also lead to distinct improvements in the OLED properties.
According to the prior art, matrix materials used for phosphorescent emitters in organic electroluminescent devices include carbazole derivatives and dibenzofuran derivatives. JP 2012-049518, U.S. Pat. Nos. 7,935,434 and 8,221,908 disclose dibenzofuran derivatives substituted by two N-phenylcarbazolyl groups. WO 2014/081206 discloses compounds in which two carbazolyl groups, one of which is substituted on the nitrogen atom by an electron-deficient heteroaryl group, are joined to one another via an arylene group.